Photos: Thick Green Algae Chokes Beach—Swimmers Dive In

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Photos: Thick Green Algae Chokes Beach—Swimmers Dive In

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Children swim through algae-choked waters off the coast of Qingdao, in eastern China's Shandong Province, on July 17.

An algae bloom, or "green tide," has clogged nearly 7,700 square miles (20,000 square kilometers) of the Yellow Sea (see map), Chinese authorities said Sunday, according to the state-run media outlet Xinhua.

The algae blanketing the beaches belongs to a species of marine plankton known as Enteromorpha prolifera, found in waters all around the world. In the right conditions, the algae can explode into so-called macro-algal blooms, Steve Morton, a marine biologist at the U.S. National Oceanic and Atmospheric Administration (NOAA), told National Geographic News in 2010.

Such massive blooms require warm ocean temperatures and waters rich in the elements phosphorus and nitrogen, which are found in fertilizers and can be carried to the coasts by water runoff. While the algae aren't toxic, big blooms can create oxygen-poor "dead zones" in the water and leave an unpleasant odor on beaches.

Tourists play in algae mats along the Qingdao, China, coastline on July 17.

In 2003 a NASA satellite spotted a green splotch in Lake Erie that turned out to be a algae bloom. And since China's blooms are much worse than anything experienced in the U.S., it's "very likely" they're also visible from space, Morton said in 2010.

China is notorious for its algae blooms. During the 2008 Summer Olympics (pictures) in Beijing, a sailboat race was almost canceled because of an outbreak. "They had thousands of people raking the ocean to get the algae out," NOAA's Morton said in 2010.

"It was an amazing sight."

Photograph from China Daily, Reuters

Washed Up

Clumps of algae lie on a Qingdao beach on July 16.

Algal blooms washed onto shore can give off a stench of rotten eggs or worse, NOAA's Morton said. The smell is caused by the release of methane and sulfur as the blooms decompose.

Photograph by Huang Jiexian, Color China Photo/AP

Child's Play

A child plays with algae-laced sand on a beach on July 16 in Qingdao.

Although the algae aren't toxic, NOAA's Morton recommended that swimmers stay away it if possible.

"Any time you have a discoloration of water, your best bet is not to swim in it," he said.

Photograph by Huang Jiexian, Color China Photo/AP

Algae Cleanup

A fisher gathers up algae to remove it from the water in Qingdao on July 6.

The North China Sea Marine Forecasting Center recently predicted the thick masses of algae would continue spreading north, according to Xinhua.